X-ray apparatus



Oct. 15, 1940. K, B|$HQFF HAL 2,217,939 I X-RAY APPARATUS Filed Oct. 7.1957 2 sheets-Snead Patented Oct. 15, 1940 UNITED" STATES X-RAYAPPARATUS Kurt Bischofl' and Karl Silbermann, Erlangen,

Germany, assignors to the firm Siemens- Reiniger -We rkeAktiengesellschaft, Berlin,

Germany Application October 7, 1937, Serial No. 167,696

In Germany October 19, 1936 18 Claims. (01. 250103) The presentinvention relates to Roentgen or X-ray apparatus, and is particularlyconcerned with arrangements for preventing overloading the Roentgentube. These arrangements lend themselves advantageously to a new methodof operating such tubes, with better results than have been attainedheretofore,

The temperature of the focal spot of a Roentgen tube must not exceed acertain value, in

' order to avoid danger of destroying the anode, or at least doing itserious damage. Devices andcontrol means have been suggested in-the pastwhich attempt to avoid the overloading of a Roentgen tube either bydisconnecting the tube when the highest possible temperature of theanode is exceeded, or by regulating the tube current in such a mannerthat the temperature of the anode is maintained approximately at thehighest permissible value during the entire operation of the apparatus.However, such devices have been found unsatisfactory and objectionablein several respects, since they do not provide either for adisconnection of the tube which a is free of delay, or for asubstantially continuous be used and installed in Roentgen apparatus.

which is already in operation and may be grounded in apparatus where theanode of the tube is connected to a high tension current source. Thatis, in the case of a Roentgen tube having an anode operating at highpotential, which is arranged within a high tension insulating andradiation- .protecting housing with groundedwalLthe ar- 45-rangementaccording to the invention may be carried out in such a'manner that theoptical system and .the light-sensitive device are at ground potential,with the light rays emanating from the focal spot of the Roentgen tubedi- 50 rected through an aperture or opening in the housing.

invention is useful for disconnecting the Roentgen tube when a certainpermissible maximum focal spot temperature is reached or exceeded, andhas the particular advantaf'e that the control of the tube current forthe purpose of using a photoelectric cell" or other light-sensitiveconnection and disconnection of the Roentgen tube current may beobtained by means of a grid-controlled valve provided either in theprimary or the secondary circuit of the high tension transformer. Thesubstantially instantane- 5 ous disconnection of the Roentgen tube .canbe accomplished in such a case by the use of relay means which operatewithout delayand which is actuated when the load limit is reached.-Permanent interruption or disconnection of the 10 Roentgen tube currentmay be obtained upon operative actuation of the lightfsensitive deviceby using suitable switching means, for example, of the stay-put orlocking type, and corresponding circuits.

It is of importance for the practical realization of the invention toprovide means for separating the Roentgen rays emanating from the focalspot 'of the X-ray tube from the light-sensitive device or preventingsuch rays from reaching the 20 device. The lenses used in the opticalsystem may for this purpose be made of lead glass, for example, "or amirror may be arranged in the path of therays from the focal spot, whichdeflects the light rays to the light-sensitive means, or photoelectriccell, the latter being properly located at the side of the apparatus.

Instead of disconnecting the Roentgen tube at the moment'when thehighest permissible focal spot temperature is reached or exceeded, theinvention may be used as previously intimated, so as to maintain thefocal spot temperature substantially constant at a desirable value. Thisobject may be accomplished by regulating the Roentgen tube currentdirectly and substantially without delay in dependence on or as afunction of the focal spot temperature. The Roentgen tube is equipped inthis case with a control grid by means of which the light-sensitivedevice regulates the current flowing through the Roentgen I tube in sucha manner that the temperature of the focal spot cannot exceed a certainpredetermined value.

- Particularly advantageous is an arrangement whereby the lightsensitive device regulates the 5 heating of the Roentgen tube so thatthe luminosity of thefocal spot remains substantially constant. This maybe accomplished by disconnecting or diminishing the heating of theRoent-- gen tube under the control of the light sensitive device whenthe focal spot reaches a certain degree of luminosity, the re-connectionor increased heating taking place upon decrease of luminosity 'of thefocal spot below an adjustable value or after the lapse of a certainadjustable time period.

The heating of the Roentgen tube is, in this form of practicing theinvention, preferably considerably increased or accelerated for thepurpose of quickly reaching the load limit. If this greatly acceleratedheating of the Roentgen tube would take place prior to connecting thehigh tension, the focal spot would be initially overloaded because thefilament temperature would not drop quickly enough to the permissiblevalue due to the inertia of the filament. The arrangement is for thisreason operated so that the heating current is connected to the Roentgentube upon starting the exposure simulaneously with connecting the hightension. so that the filament temperature is rising at that moment.

Inasmuch as the light sensitive device takes care that the filamenttemperature can never exceed the highest permissible value (since thefocal spot luminosity would otherwise also rise to an impermissiblevalue), it follows that the heating current can be increased-as desired,so that the speed with which the cathode and, therefore, also the focalspot reach the highest permissible temperatures can be accelerated atwill. It is therefore entirely possible to heat a cathode intermittentlywith a current of, for example, 12 or more amperes, whose maximumpermissible permanent heating current is about 8 amperes.

A milliampere-second relay is preferably provided, which disconnects thehigh tension connected to the Roentgen tube as soon as amilliampere-second product is reached which has previously been adjustedon this relay. The use of a known device for disconnecting the Roentgentube as soon as a sufliclent blackening of the fllm is accomplishedincident to the exposure, is also very advantageous.

The heating of the Roentgen tube takes place preferably from a directcurrent source, or from an alternating current source of high frequency,in order to avoid the oscillations of the emission caused by the use ofan alternating current of, for example, 50 cycles, thereby accomplishingmore accurate work.

In order to protect the Roentgen tube, the light sensitive cell isgenerally adjusted to a value which lies below the load limit. In orderto prevent destruction of the Roentgen tube due to failure of theequipment, a second light sensitive device, e. g., a photoelectric cell,may be, provided which disconnects the Roentgen tube when the highestpermissible luminosity of the focal spot is exceeded. v

The above stated and other objects and features of the invention willappear from the detailed description presented below with reference tothe accompanying drawings. In these drawmgs,

Figs. 1, 2 and 3 show three diiferent embodiments of the invention,wherein the Roentgen tube is disconnected at the instant when the focalspot temperature reaches a predetermined va ue;

Fig. 4 shows by means oftwo curves the variation of the temperature ofthe focal spot in relation to the load time;

Fig. 5 shows a practical structure wherein the Roentgen or X-ray tube isenclosed in a high tension insulating and radiation protecting groundedhousing with means for transmitting the light rays from the focal spotthrough an optical system to the light-sensitive device.

The apparatus is represented in the drawings, except Fig. 5, in aconventional and more or less schematic manner. The general structureand operation of individual devices, such as photoelectric cells,electronic valves, gaseous discharge tubes, and others, as used inconnection with the various structures herein described, is well knownand will not be dwelled upon in detail except when necessary for anunderstanding of the invention.

Referring now to the embodiment shown in Fig. 1. the Roentgen tube isindicated at I. It receives current from the high tension transformer 2which may be connected to the current source 4 by means of a switch 3.The light rays emanating from the focal spot of the Roentgen tube l aredirected over an optical system 5 to a photoelectric cell 6 which islocated in a circuit of the relay 1; this circuit being provided with abattery, as indicated. The lens or lenses used in the optical system maybe made of lead glass. Relay 'I-is provided with an armature adapted toclose the circuit for the relay I which operates the switch 8. In otherwords, when the contact of relay 1 is closed, relay 8 is energized andthe switch 3 opens its contacts, disconnecting the current source 4 fromthe primary winding of the transformer 2. Current for the Roentgen tubeI is thus disconnected. The actuation of relay 1 is dependent, on theactivation of the light-sensitive device 6 which is energized by thelight rays from the focal spot of the Roentgen tube through the mediumof the optical system 5. at the instant when the focal spot temperaturereaches a critical value and produces light rays of suflicient intensityto activate the light-sensitive device 6. The high tension transformer 2is thus disconnected from the current source and the Roentgen tubeceases to operate for a short interval, or until the focal spot hascooled off enough to reduce the light reaching photo cell 8 suflicientlyto allow relay I to deenergize.

The embodiment shown in Fig. 2 comprises a Roentgen tube II, the hightension transformer l1, and a current source It However, in the primarycircuit of the transformer there is pro vided a valve or tube 9 whichtakes the place of the switch 3 used in the previous embodiment. Thegrid of this valve 9 is controlled from the valve I 0, the latter beingconnected in a closed. circuit, as shown in the drawings, and governedin its operation by the "light-sensitive device It,

which may again be a photoelectric cell or the like. Current flowing inthe cell i6 (depending, of course, on the light rays striking the cellaccording to the intensity of the temperature of the focal spot of theRoentgen tube) changes the potential of the upper terminal of theresistance ii. The potential at thispoint becomes less negative with anincrease in the current flow through the cell, and when the currentreaches a certain value the normal negative grid bias at the valve I0 isreduced enough so that the valve becomes conductive. This in turn causesa current flow in the plate circuit of valve Ill, including theresistance l2, and the grid of the valve 8 changes from positive tonegative, whereupon the discharge through the valve ceases. Since thistube is in the primary circuit of the transformer 2, the Roentgen tubeIt connected in the secondary circuit is deprived of current and ceasesto operate. As in the previous case, operation is resumed as soon as thefocal spot in the Roentgen tube has cooled off somewhat.

The manner of transmitting the light rays from the focal spot of theRoentgen tube II to the photoelectric cell I6 is apparent from thedrawing Fig. 2. The light rays first strikethe mirror i3 from strikingthe cell It.

and are reflected laterally toward the photoelecr "the quality of theRoentgen picture and without trio cell I6 through the optical system IS.The

Roentgen rays emanating from the Roentgen tube M are not reflected andare thus prevented Thearrangement disclosed in Fig. 3 comprises theRoentgen tube 20 connected to the secondary winding of the transformer2|, the primary of which is connected to the current source 29. The

connection and disconnection of the Roentgen tube are taken care of inthis case by the gridcontrolled switching valve 22 connected in serieswith the Roentgen tube in the circuit of the secondary winding of thetransformer 2|. The light rays from the focal spot of the Roentgen tube20 strike the mirror 26, which reflects them through the optical system21 and a suitable shutter, as indicated, to the light-sensitive device28. As in the previous embodiments, the light rays, varying inintensity, cause a current flow through the photoelectric cell inaccordance with the temperature of the focal spot. In the present case,however, when current flows through the photo cell, the grid of the tube25 becomes more negative,

which reducesor prevents current flow in the plate circuit of the tubeandcauses the grid of the tube 24 to become positive with respect to itscathode. As a result, the tube 24 is rendered conductive, and a suitablecontrol or transmitting device 23 is operated to place a negativepotential on the grid of the tube 22. Any known arrangement foreffecting this purpose may be used and accordingly the same has not beenshown in detail, being represented in the drawings merely by arectangle. The negative potential on the grid of the switching valve 22renders the tube non-conductive and thus cuts off the current to theRoentgen tube 20. The switching actions described herein aresubstantially without any delay, once the critical temperature isreached.

In Fig. 4 two curves a and b are shown, which illustrate how thetemperature T of the focal spot rises as a function of the load time t.'Curve a. shows what happens when the input to the Roentgen tube is suchthat a moderately rapid rise in temperature occurs. When the highestpermissible temperature T1 is reached, the current to the Roentgen tubewill be interrupted, whereupon the temperature of the focal spot willdrop quickly in accordance with the curve a. When the temperature of thefocal spot reaches a certain adjustable value T2, the relay orvalvewhich is used vre-establishes the current flow through the Roentgen tubeand the temperature again rises to the maximum allowed. The relay orvalve thus disconnects and connects current to the tube periodically andmaintains the temperature of the focalspotbetween the values T1 and T2.Curve 1; is similar to curve a, but corresponds to a higher input to theRoentgen tube and a more rapid heating. By comparing the curves, it willbe seen that in the'second case the maximum temperature T1 is reachedinless than half the time required in the first case. The cooling rate,shown by curve b, is of course the same as the cooling rate indicated bya.

It is particularly advantageous to repeat the disconnection andreconnection of the current through the Roentgen tube until apredetermined milliampere-second product is obtained which has beenpreviously adjusted on a suitable milliampere-second relay. Thisfurnishes the possibility of adjusting the values which determine theload of the Roentgen tube, namely, voltage, current and exposure time,solely with respect to any danger of overloading the Roentgen tube. Itis also possible, as indicated in Fig. 4, curve b,

to accelerate the heating of the Roentgen tube so much that thetemperature of the focal spot rises very quickly without danger ofoverloading the Roentgen tube. Such a rapid heating is of advantage inmaking an exposure, because the transition period from the starting-upof the Roentgen tube to penetration of the object and actual exposure isconsiderably shortened, and a definite milliampere-second product isreached in a shorter time.

In Fig. 5 is shown a practical embodiment of the invention wherein theRoentgen tube, the tube M in Fig. 2, for example, is provided with ahigh tension insulating and radiation-protecting housing 50.v the outerwall of which-is grounded. The light rays emanating from the Roentgentube .are transmitted through an opening 5| of the housing to theoutside and strike the mirror III which is located within the groundedshutter housing 52. The light rays are then conducted through theoptical system l5 to the removably mounted light-sensitive cell It. Theoptical system l5 and the light-sensitive cell l6 are therefore atground potential, as they are mounted on the grounded housing 50.

The various devices shown in Figs. 1 to 3 may, however, be mounted inany convenient and suitable manner so long as the relation of theequipment is maintained as indicated and described,

for the purpose of obtaining the desired explained 3 results. Fig. 5merely shows one example of how the parts may be arranged.

What is desired to have protected by,Letters Patent of the United Statesis particularly pointed out in the appended claims.

We claim:

1. Apparatus for controlling the operation of a Roentgen tube,comprising means for controlling the supply of operating current to thetube, and means including a light-sensitive element responsive tolight-emitted from the focal spot of the tube for controlling said firstmeans.

2. Apparatus for controlling the operation of a Roentgen tube,comprising a switch for cutting oif the supply of operating current tothe tube,

and means including a photoelectric cell responthe ' said tube, a mirrorfor reflecting light from the focal spot of the tube to said cell, andmeans controlled by said cell for controlling the current supply to saidtube.

5. Apparatus for controlling the operation of a Roentgen tube,comprising a photoelectric cell located within the range of X-nays andlight rays thrown off from the focal spot in said tube, an opticalsystem impervious to X-rays for directing light rays to said cell, andmeans controlled by.

said cell for controlling the supply of power to said tube. I

6. Apparatu for controlling the operation of a Roentgen tube, comprisinga photoelectric cell responsive to light emanated from the focal spot ofsaid tube, and means controlled by said cell for maintaining thetemperature of the focal spot between a maximum and minimum value byperif odically disconnecting and connecting the supply of power for thetube.

7. Apparatus for controlling the operation of a Roentgen tube,comprising a space discharge device having a control grid, meansincluding a photoelectric cell responsive to light emanated from thefocal spot in said tube for controllin the potential on said grid, andmeans controlled by said device for cutting off the supply of power tosaid tube when the focal spot temperature reaches a certain value andfor re-connecting it when the temperature falls below a certain value.

8. Apparatus for controlling the operation of a Roentgen tube,comprising a light-sensitive device responsive to light emitted from thefocal spot of said tube, and means controlled by said device forregulating the supply of power to said tube by reducing the power whenthe light emitted reaches a certain value and increasing the power whenthe amount of light drops below said value.

9. Apparatus for controlling the operation of a -Roentgen tube,comprising means for connecting and disconnecting the supply of power tosaid tube, and means dependent upon the intensity of light emitted fromthe focal spot of said tube for controlling said connecting anddisconnecting means.

10. The combination, with a Roentgen tube,

A and a source of power therefor, of a protective housing for said tubehaving a grounded outer wall, an optical system and a photo cell mountedon said housing, said optical system being so positioned that itreceives light through an opening in the housing from the focal spot ofthe tube and transmits said light to said photo cell, and means Icontrolled by said photo cell for governing the supply of power to saidtube.

11. The method of operating a Roentgen tube, which consists in testingthe' amount of light emitted from the focal spot while the tube is inoperation, and shutting off the power supply to the tube when the lightemitted reaches a certain predetermined value.

12. The method of operating a Roentgen tube, which consists incontinuously testing the amount of light emitted from focal spot whilethe tube is in operation, reducing the power supplied to the tube whenthe light emitted exceeds a certain value and increasing the powersupplied to the tube when the light emitted falls below said value.

- 13. The method of preventing the overloading of a Roentgen tube, whichconsists in separating the light rays generated at the focal point insaid tube from the X-rays produced at said spot, directing said lightrays to a photoelectric cell, and regulating the load on said tube inaccordance with the resistance of said cell under the action of saidlight.

14. The combination, with a Roentgen tube and a switching device forcontrolling the supply of power thereto, of a photoelectric cell, anoptical system for receiving visible light from the focal spot of saidtube and for transmitting it to said cell, and means including said cellfor controlling said switching device.

15. The combination, with a Roentgen tube and a source of power foroperating it, of a photoelectric cell, an optical system having aselective said cell, and means including said cell for controlling saidswitching'device.

17. The combination, with a Roentgen tube and a circuit over which hightension operating potentials are supplied to'the anode thereof, of aspace discharge device included in said circuit, a photoelectric cell,an optical system for transmitting light from the focal spot in saidtube to said cell, and means including said cell acting under theinfluence of said transmitted light for rendering said discharge devicenon-conductive.

18. The method of operating a Roentgen tube, which consists in supplyingan excess amount of power to the tube to enable the same to quicklyreach an efficient operating condition, in testing the amount, of lightemitted from the focal spot while the tube is in operation, and shuttingoif the power supply to the tube when the light emitted reaches acertain predetermined value, thereby preventing the excess power fromdamaging the tube.

KURT BISCHOFF. KARL SILBERMANN.

